Multiplex telegraphy.



F. K. VREELAND. MULTIPLEX TELEGRAPHY. APPLICATION FILED JUNE 4. 1913.

1,171,814. Patented Feb. 15, 1916. '1 \I- 8 v Witnesses Inventor ttomeys.

UNITED STATES PATENT OFFICE.

FREDERICK K. VREELAND, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO VREELAND APPARATUS COMPANY, INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MULTIPLEX TELEGRAPHY.

Specification of Letters Patent.

Patented Feb. 15, 1916.

To all whom it may concern:

Be it known that I, FREDERICK ICVREE- LAND, a citizen of the United States, residing at Montclair, in the county of Essex and State of New Jersey, have invented a certain new and useful Improvement in Multiplex Telegraphy, of which the following is a specification.

This invention relates to the system of multiplex telegraphy described in my applications, Serial No. 497194, filedMay 20, 1909 I and Serial No. 536963, filed January 8, 1910, wherein a number of alternating currents of difierent frequencies are simultaneously impressed upon a common line and selectively received by a number of receiving units, each tuned to respond to one of the transmitted frequencies; and its object is to further simplify and perfect that system.

In the drawing, Figure 1 illustrates in diagram a system of multiplex telegraphy embodying my invention and Fig. 2 is a view in section of a form of transformer suitable for use in the system.

In Fig. 1 is represented a line having a plurality of sending and receiving sets at each end, sets 1, 2 and 3 being located at one end of the line,'and sets 4:, 5 and 6 at the other end of the line. Sets 1, 2, 5 and 6 are represented diagrammatically, for the sake of simplicity, by their sifting circuits alone. In sets 3 and 4 I have illustrated, with greater detail, one form of a combined sending and receiving set, which may be regarded as typical of the various alternative forms of the apparatus described in my former applications.

In my application Serial No. 497194;, I have described, as one of the important features of the invention, a plurality of tuned sifting circuits,-shunted across or connected in parallel relation to the line, each sifting circuit having a large unbalanced reactance relative to the line impedance, at the nearest foreign frequency. In that application, I have shown the sifting circuits connected in parallel relation to the line by a direct metallic connection.

In my application, Serial No. 536963, I have shown a modification in which a sifting circuit is shunted across the line, not by a directmetallic connection, but through a transformer of unequal windings, which permits the large unbalanced reactance'relative to the line impedance to be secured without the use of such large individual inused.

ductance and capacity reactances as are required when a direct metallic connection is In the present invention, still greater simplicity and effectiveness are secured by using a single transformer of unequal windings for connecting, in parallel relation to the line, a plurality of sifting circuits, with their associated sending and receiving apparatus.

In Fig. 1, a line is shown having at each end a transformer of unequal windings, P, S. The high voltage winding of each transformer is connected to the line, and the low voltage winding of each is connected to a local or auxiliary line A, B, Across these local or auxiliary lines, the various sending and receiving sets are connected in parallel.

In the two sets, 3 and 4, which are shown in greater detail, there are bifurcated sifting circuits comprising the main inductance L the capacity C and the double contact key K, which makes contact through the contact a with the sending branch, including the secondary coil S whereby power is drawn from the oscillator O, and the primary coil P whereby the transmitted signals are communicated to the receiver. The key also makes alternative contact through the contact I), with the receiving branch containing the primary coil P whereby re ceived signals are communicated to the receiver. Both coils P and P are in inductive relation with the} coil S which operates also as the inductance of the tuned receiving circuit S R, including the electrostatic receiver R, which operates also as the capacity whereby the circuit is tuned. The sifting circuit L C, K of set 3,'and the sifting circuits of sets 1 andf2, are connected in parallel relation to the auxiliary line A, B, and also, through the transformer S P, to the main line. In like manner, the sifting circuits of sets 4, 5 and 6 are connected in pagallel relation to the line at its distant en The inequality of the windings P S of the transformers, not only makes the potential differences across the auxiliary lines A, B, A, B smaller than those across the main line, but it has the further effect of multiplying all the reactances of its associated circuits with respect to the main line, so that the requisite, large unbalanced reactance for foreign frequencies, relative to the line impedance, may be secured with relatively small absolute values of the inductance and capacity reactances. In this way, I eliminate altogether the tendency to large voltages across the inductance coils and the condensers, which in my first application (and in part in my second application) is avoided by subdividing the capacity and inductance units, and I simplify andreduce the cost of the apparatus by reducing the number of turns of wire in the coils and by avoiding a multiplicity of transformers.

The transformer P, S differs from the other transformers in the system in an important particular. The transformer P 8, or P S for example, is a transformer of unequal windings, and in the case of the coil P the coupling with the secondary S, is much closer than that of the coil P with S In either case, however, the coupling is essentially a loose one, so that the tuned resonant circuit 8 R may oscillate freely, and thus secure its full measure of selectivity. The function of the transformer P, S, however, is quite difierent. In this case, freedom of selective resonance is not required; but rather, a rigid connection of the auxiliary line A B or A B, with the main line, so that the oscillations transmitted are forced oscillations, and the auxiliary line be comes, in effect, an extension of the main line, on which, however, voltages, reactances, etc., are changed by a multiplying factor, depending upon the ratio of transformation of the transformer P, S. To this end, the transformer P, S should be closely coupled. I prefer to use a transformerhaving a core of very fine iron wires severally insulated with enamel,-as illustrated in Fig. 2, in which the core is shown by D and the high and low voltage windings by P, S.

Close coupling is further important, inasmuch as the high voltage circuit is not tuned, and the reactance of the winding P would tend to reflect the incoming signals and prevent them'from passing through it, if it were not for the effect of the secondary coil and its associated circuits. The secondary, however, by virtue of the large mutual induction of a closely coupled transformer, has the effect of neutralizing the self-induction of the primary P, at any frequency for which there is a sifting circuit in which the reactances have been balanced by tuning to that frequency. Currents of any frequency for which there is a sifting circuit will, therefore, pass freely through the transformer P, S in either direction, and the working of the auxiliary lines A B and A B will be equivalent to that of the main line, except as it is modified by the ratio of transformation of the transformer. The main line with its simple aperiodic high voltage winding becomes, in effect, a part of the complex tuned low voltage system, whose parts, including the transformer windings, are proportioned with reference to the line constants to secure the requisite selectivity. Any of the forms of apparatus which, in my former applications, I have shown connected to the line by a direct metallic connection, can be used with similar effect in the present arrangement, the inductance, capacity, and other reactances of the sifting circuit being so chosen as to have the requisite value with respect to the line when multiplied by the square of the ratio of transformation of the transformer.

What I claim is 1. In a system of multiplex telegraphy by alternating currents of different frequencies, the combination with a line, of a transformer having a simple aperiodic high voltage winding connected to the line and a low voltage winding forming part of a complex tuned low voltage system whereby the self induction of the transformer is neutralized at a plurality of definite frequencies, substantially as set forth.

2'. In a system of multiplex telegraphy by alternating currents of different frequencies, the combination. with a line, of a transformer of unequal windings having its high voltage winding connected to the line and a plurality of tuned sifting circuits connected in parallel to the low voltage winding of the transformer, said transformer being adapted to pass simultaneously and without reflection the currents transmitted and received by the several sifting circuits and transmitting and receiving means associated with the sifting circuits, substantially as set forth.

3. In a system of multiplex telegraphy by alternating currents of different frequencies, the combination with a line, of a transformer of unequal windings having its high voltage winding connected to the line and a plurality of tuned sifting circuits connected in parallel to the low voltage winding of the transformer and having when thus connected a large unbalanced reactance for small frequency differences relative to the equivalent line impedance, said transformer being adapted to pass simultaneously and without reflection thecurrents transmitted and received by the several sifting circuits and transmitting and receiving means associated with the sifting circuits, substantially as set forth.

This specification signed and witnessed this second day of June, 1913.

FREDERICK K. VREELAND. Witnesses:

J. F. COLEMAN, ANNA E. RENTON. 

